I can't understend pls help me??

Question about the task

Task about algorithms

Java Syntax, Level 9, Lesson 11

Resolved

i am stuck with this.

Task: The user enters a list of words (and numbers) from the keyboard. The words are displayed in ascending order, the numbers in descending order.

Example input:
Cherry 1 Bob 3 Apple 22 0 Watermelon

Example output:
Apple 22 Bob 3 Cherry 1 0 Watermelon

Requirements:

The program must read data from the keyboard.
The program should display data on the screen.
The displayed words should be sorted in ascending order (using the provided isGreaterThan method).
The displayed numbers must be sorted in descending order.
The main method should use the sort method.
The sort() method should call the isGreaterThan() method.
The sort() method should call the isNumber() method.

package com.codegym.task.task09.task0930; import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.ArrayList; /* Task about algorithms */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); ArrayList<String> list = new ArrayList<String>(); while (true) { String s = reader.readLine(); if (s.isEmpty()) break; list.add(s); } String[] array = list.toArray(new String[list.size()]); sort(array); for (String x : array) { System.out.println(x); } } public static void sort(String[] array) { // write your code here for (int i=0; i<array.length; i++){ if (isNumber(array[i]) == true){ for(int j=i+1; j<array.length; j++){ if (isGreaterThan(array[j],array[i])){ String temp = array[i]; array[i] = array[j]; array[j] = temp; } } } else { for (int b=i+1; b<array.length; b++){ if (isGreaterThan(array[i],array[b])){ String temp = array[i]; array[i] = array[b]; array[b] = temp; } } } } return ; } // String comparison method: 'a' is greater than 'b' public static boolean isGreaterThan(String a, String b) { return a.compareTo(b) > 0; } // Is the passed string a number? public static boolean isNumber(String s) { if (s.length() == 0) return false; char[] chars = s.toCharArray(); for (int i = 0; i < chars.length; i++) { char c = chars[i]; if ((i != 0 && c == '-') // The string contains a hyphen || (!Character.isDigit(c) && c != '-') // or is not a number and doesn't start with a hyphen || (i == 0 && c == '-' && chars.length == 1)) // or is a single hyphen { return false; } } return true; } }

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Sela

Level 20 , Poland

9 July 2020, 10:10

1. you're sorting numbers in ascending order - should be in descending - this is easy to achieve if you first separate Strings from numbers. 2. you're not allowed to mix the places reserved for Strings with those reserved for numbers. you could gain this in following steps: - separate String and numbers simply putting them in different arrays or ArrayLists, but keep the original one to know what is stored under certain index (String or number) - then sort them using different approach for numbers and String (remember to sort numbers in descending order) - and finally join sorted Strings and numbers back to original array checking what certain index in original array holds (String or number).

Tata

Level 16 , Hisar, Haryana, India

9 July 2020, 12:02

Hi Sela 🙏, Thank you for your reply. I have sorted both number and string in seperated array.

ArrayList<Integer>  number = new ArrayList<Integer>();
        ArrayList<String> string = new ArrayList<String>();
        for (String checkNum : array){
            if (isNumber(checkNum)== true)
                number.add(Integer.parseInt(checkNum));
            else
                string.add(checkNum);
        }

        Collections.sort(number);
        Collections.reverse(number);

        for (int i=0; i<string.size(); i++){
            for (int j=i+1; j<string.size(); j++){
                String temp = string.get(i);
                String a = string.get(i);
                String b = string.get(j);

                if (isGreaterThan(a,b)){
                    a = b;
                    b = temp;
                }
            }
        }
    }

Now, could you tell me how to join both of them acc. to right index. pls.

Sela

Level 20 , Poland

9 July 2020, 15:10

1. you do not have to sort numbers ascending - line no 10 can be removed, reverse is enough - line no 11 does the job 2. your bubble sort solution for strings is not adapted for ArrayList. the assignment

a=b;

on line 20 means only that now a refers to String b but nothing changes in ArrayList. better use the method

set(index, String)

the code would look like follows:

for (int i=0; i<string.size(); i++){
            for (int j=i+1; j<string.size(); j++){
                String temp = string.get(i);
                String b = string.get(j);
                if (isGreaterThan(temp,b)){
                    string.set(i, b);//setting the index in ArrayList differs from that in Arrays
                    string.set(j, temp);
                }
            }
        }

3. sort method in this task as an argument passes the reference to the array so let's join Strings and numbers directly in it:

//put back sorted numbers and strings into array in places of strings and numbers respectively
       int j = 0, k = 0;//different count for number and string ArrayList
       for (int i = 0; i < array.length; i++) {
           if (isNumber(array[i])){//checks if it is a number
               array[i] = String.valueOf(number.get(j));//convert number back to String
               j++;
           }else {
               array[i] = string.get(k);
               k++;
           }
       }

hope it helps

Tata

Level 16 , Hisar, Haryana, India

10 July 2020, 13:05

thank you very very much to help me to solve this task.😊😊

Sela

Level 20 , Poland

10 July 2020, 15:39

my pleasure